1. Field of the Invention
This invention relates to new and improved motion sensors and, more particularly, to non-gyroscopic sensors for measuring inertial angle.
2. Brief Summary of the Invention
This invention concerns a sensor of a non-gyroscopic type which depends upon the kinematic coupling of an angular rate vector to an inertia bearing annulus in which sensing of the angular rate is accomplished by a fluid. For this purpose, a liquid ring is carried within a housing which is supported for rotation on a spindle axis passing through a diameter of the ring. The housing may take the form of a disc or sphere. The ring is spun about this axis at a constant angular velocity. While the ring is so spinning, the imposition of an angular rate vector normal to the axis of the spinning will produce a circumferential displacement of the fluid annulus relative to its housing. The angular rate of this displacement is proportional to the rate of change of sensed angular velocity (angular acceleration) produced by the kinematic coupling. Implicit in the transformation of this vector onto the rotating frame of the liquid annulus where it interacts with the dynamics of the ring to produce the noted circumferential motion. In effect, the constant input rate vector is harmonically modulated by the kinematic coupling action.
Motion of the annulus fluid is detected electrically by direct coupling, through conductive properties of the fluid, to eddy currents generated in the fluid as it moves through the field of a magnet affixed to the housing of the liquid annulus. The signal voltage so generated is proportional to the velocity of fluid circulating around the annulus, giving an output proportional to kinematically coupled angular acceleration. Note that the annular accelerator produced by the kinematic coupling is proportional to the constant rate vector input. The signal so generated is transferred through the suspension of the disk to synchronous demodulators for spatial resolution into voltages referred to two axes which are perpendicular to each other and to the spindle axis of the disk. The two voltages so produced provide a measure of any rate vector or vectors applied in a plane normal to the spindle axis of the liquid annulus bearing structure.
The present invention utilizes an angular accelerometer of the type described above as the fundamental inertial element for sensing angular velocity about one or more axes. The rate sensor is mounted in gimbals which, positioned in response to signals generated by the inertial rate sensor, enable the measurement of steady state as well as time variant effects including rate and angular displacement. By synchronous demodulation, signals derived from the sensor are resolved into in-phase and quadrature components relative to the spindle reference axis. Signals representative of the DC analogue of rate for two independent and orthogonal rate vectors are thus derived. These signals are each dynamically processed and then applied to torquers mechanically implemented to act upon the gimbal set. The torquers operate in a direction which reduces the error signal supplied to them to zero. The gimbals are instrumented with angle transducers which permit observation of the position of the gimballed sensor relative to the frame upon which it is mounted.
3. Prior Art
In U.S. Pat. No. 3,618,399, a concept is described which provides a means for measuring angular velocity through kinematic coupling. The apparatus disclosed, however, does not provide for direct measurement of angular change of position.
Another aspect of prior art is disclosed in U.S. Pat. No. 3,960,691. Here, the liquid ring and housing is used in a non-rotating mechanization to provide for the measurement of transient or oscillatory effects. As such, it does not suffice for the many applications which require measurement of steady state effects.
It is an object of the present invention to meet the above identified needs .